But what is the initial condition here? {{MATH_16}} does not apply, because {{MATH_17}}. But we know that the solution, {{MATH_18}} has to be a differentiable function. Therefore, {{MATH_19}} is continuous. So, it is , in particular, continuous at {{MATH_20}}. Therefore, using the expression for {{MATH_21}} for {{MATH_22}} in {{MATH_23}}, we get that